FIELD OF THE INVENTION
This invention relates to a process for producing a non-aqueous liquid dispersion of polymer made with a polymeric peroxide comprising a block copolymer or block copolymers dispersed homogeneously with splendid stability in an organic liquid.
In general, a non-aqueous system dispersion of polymers is useful in the fields of paints, inks, adhesives and the like as a coating composition having characteristic features of low viscosity and a high content of solid ingredients.
Use of such a non-aqueous system dispersion of polymers, especially in the field of paints, makes it possible to reduce the amount of solvent to be used and to replace conventional solvents with photochemically inactive solvents. For this reason, great future developments are expected for the dispersions as a paint having reduced pollution effects.
Most of the non-aqueous system dispersions of polymers which have been available, are dispersions prepared by polymerizing in an organic liquid a vinyl type monomer which is converted to a polymer insoluble in the organic solvent, employing a polymer soluble in the organic solvent as a dispersion stabilizer. The thus-prepared dispersion comprises the product polymer and the dispersion stabilizer, both of which are homogenously dispersed in the organic liquid.
As to the features of the polymers, it can be said that in the polymerization, active polymerization sites are formed on a part of the stabilizer molecules and react with a small part of the vinyl type monomer to be converted to the polymer insoluble in the organic liquid (hereinafter the latter polymer is referred to as insoluble polymer) to produce a block or graft copolymer consisting of a soluble polymer part originating from the dispersion stabilizer and an insoluble polymer part originating from the vinyl type monomer, and also that, at the same time, most parts of the vinyl type monomer which are subjected to polymerization do not take part in the block or graft copolymerization and are homopolymerized to produce the insoluble polymer.
As to the conventional non-aqueous system dispersion of polymers, there are problems that the solution has a low dispersion stability, since the solution contains a small amount of the above mentioned block or graft copolymer which is excellent in dispersion stability and contains a large amount of the above stated homopolymerized insoluble polymer, which is merely dispersed in the organic liquid by secondary physical bondings between the homopolymerized insoluble polymer and the block or graft copolymer. There are great problems, especially in the case in which the thus obtained non-aqueous system dispersion of polymers is used as a component for forming coating films.
As a result, the classes of vinyl type monomers which are usable for forming the insoluble polymer are restricted, since the block or graft copolymer and the insoluble polymer should be tightly bonded to each other through secondary physical bonds between molecules for maintaining the dispersion stability and, therefore, a vinyl type monomer which can produce a highly polar and rigid polymer exerting a large secondary binding force should necessarily be used in an large amount.
Accordingly, coating films obtained from such a non-aqueous system dispersion of polymers are poor in flexibility, resistance to moisture, resistance to acid and tight adhesion to articles to be coated. In addition, particles of the insoluble polymer cannot sufficiently be fused nor fluidized on the formation of the coating films, since the particles are hard. This results in films formed in a state of containing particles, which causes a decrease in the strength of the coating films.
Furthermore, the above mentioned non-aqueous dispersion of polymers is not sufficient in physical dispersion stability. For example, application of a high shearing stress to the solution for dispersing a pigment would result in aggregation whereby to precipitate the insoluble polymer, and there is a possibility of gelation or coagulation precipitation of the insoluble polymer when a polar solvent or plasticizer which exerts a large solubility to the insoluble polymer is added into the dispersion, because the dispersion stability on storage is greatly reduced.
Essential points of the above mentioned problems lie in that the block or graft copolymer having good dispersion stability and being the minor ingredient of the dispersion is bonded with the insoluble polymer, which is the major ingredient, through secondary bonds held by physical forces working between their molecules so as to give dispersion stability to the insoluble polymer.
In order to solve these problems, there are proposed processes using reaction systems in which much larger amounts of the block or graft copolymer are produced in the reaction of the dispersion stabilizers with the vinyl type monomers.
For example, processes are disclosed which give the non-aqueous system dispersions of polymers containing large amounts of block or graft copolymers produced by the reaction of dispersion stabilizers and vinyl type monomers in such a manner that a polymerizable vinyl group is introduced into the dispersion stabilizer molecules (U.S. Pat. No. 3,607,821, Japanese Patent Publication No. 23,350/1965 and Japanese Patent Laid-Open Publication Nos. 11,397/1972 and 126,093/1975); that an additional functional group other than a vinyl group and a further functional group which has a complementary nature to the additional functional group are introduced to the vinyl type monomer molecules and the dispersion stabilizer molecules, respectively (U.S. Pat. No. 3,365,414); and that a vinyl type monomer having a solubilizing polymer part in the side chain is used as the dispersion stabilizer (British Patent Nos. 1,096,912 and 1,206,442 and Japanese Patent Laid-Open Publication No. 30,434/1974).
These processes have advantages in that insoluble polymer parts are stably dispersed as low polar polymer parts because they provide the dispersions containing large amounts of the block or graft copolymer. However, on the other hand, there are some problems in the processes in actual production, such that it is very difficult to control the polymerization reactions with the result of gelation of the products or of difficulty in promoting the reactions.
Furthemore, there is proposed in Japanese Patent Laid-Open Publication No. 5,194/1974, a process using peroxyester type organic peroxides having two peroxy bonds in the molecules whose decomposition temperatures are different from each other, in that a vinyl type monomer is polymerized in a first step in an organic liquid at the lower decomposition temperature, which monomer is convertible to a product polymer soluble in the organic liquid and then a second vinyl type monomer convertible to a product polymer insoluble in the organic liquid is graft polymerized in the second step onto the first product polymer at the higher decomposition temperature in order to produce a non-aqueous system dispersion of polymers. In this process, half of the polymers produced in the first step polymerization are homopolymers which do not contribute to the graft polymerization in the second step polymerization according to the reaction mechanism because the used organic peroxide is bifunctional and about half of the polymers produced in the second step are also homopolymers. This results in a very low efficiency in grafting and, therefore, this process is not estimated as being a preferable one.
In the conventionally and actually used non-aqueous system dispersions of polymers, freedom in selecting the vinyl type monomers forming the insoluble polymer is very restricted as explained above and the process involves problems as to the dispersion stability.
Therefore, a satisfactory polymer has not yet been obtained as a polymer for forming coating films, but technical progress is eagerly expected.